import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;
import java.util.Scanner;
 
//讓該類實現(xiàn)Runnable接口，該類的實例可作為線程的target
public class Test implements Runnable {
 // 使用常量作為本程序的多點廣播IP地址
 private static final String BROADCAST_IP = "230.0.0.1";
 // 使用常量作為本程序的多點廣播目的的端口
 public static final int BROADCAST_PORT = 30000;
 // 定義每個數(shù)據(jù)報的最大大小為4K
 private static final int DATA_LEN = 4096;
 // 定義本程序的MulticastSocket實例
 private MulticastSocket socket = null;
 private InetAddress broadcastAddress = null;
 private Scanner scan = null;
 // 定義接收網(wǎng)絡(luò)數(shù)據(jù)的字節(jié)數(shù)組
 byte[] inBuff = new byte[DATA_LEN];
 // 以指定字節(jié)數(shù)組創(chuàng)建準備接受數(shù)據(jù)的DatagramPacket對象
 private DatagramPacket inPacket = new DatagramPacket(inBuff, inBuff.length);
 // 定義一個用于發(fā)送的DatagramPacket對象
 private DatagramPacket outPacket = null;
 
 public void init() throws IOException {
 try {
  // 創(chuàng)建用于發(fā)送、接收數(shù)據(jù)的MulticastSocket對象
  // 因為該MulticastSocket對象需要接收，所以有指定端口
  socket = new MulticastSocket(BROADCAST_PORT);
  broadcastAddress = InetAddress.getByName(BROADCAST_IP);
  // 將該socket加入指定的多點廣播地址
  socket.joinGroup(broadcastAddress);
  // 設(shè)置本MulticastSocket發(fā)送的數(shù)據(jù)報被回送到自身
  socket.setLoopbackMode(false);
  // 初始化發(fā)送用的DatagramSocket，它包含一個長度為0的字節(jié)數(shù)組
  outPacket = new DatagramPacket(new byte[0], 0, broadcastAddress, BROADCAST_PORT);
  // 啟動以本實例的run()方法作為線程體的線程
  new Thread(this).start();
  // 創(chuàng)建鍵盤輸入流
  scan = new Scanner(System.in);
  // 不斷讀取鍵盤輸入
  while (scan.hasNextLine()) {
  // 將鍵盤輸入的一行字符串轉(zhuǎn)換字節(jié)數(shù)組
  byte[] buff = scan.nextLine().getBytes();
  // 設(shè)置發(fā)送用的DatagramPacket里的字節(jié)數(shù)據(jù)
  outPacket.setData(buff);
  // 發(fā)送數(shù)據(jù)報
  socket.send(outPacket);
  }
 } finally {
  socket.close();
 }
 }
 
 public void run() {
 try {
  while (true) {
  // 讀取Socket中的數(shù)據(jù)，讀到的數(shù)據(jù)放在inPacket所封裝的字節(jié)數(shù)組里。
  socket.receive(inPacket);
  // 打印輸出從socket中讀取的內(nèi)容
  System.out.println("聊天信息：" + new String(inBuff, 0, inPacket.getLength()));
  }
 }
 // 捕捉異常
 catch (IOException ex) {
  ex.printStackTrace();
  try {
  if (socket != null) {
   // 讓該Socket離開該多點IP廣播地址
   socket.leaveGroup(broadcastAddress);
   // 關(guān)閉該Socket對象
   socket.close();
  }
  System.exit(1);
  } catch (IOException e) {
  e.printStackTrace();
  }
 }
 }
 
 public static void main(String[] args) throws IOException {
 new Test().init();
 }
}